Heater cables, such as self-regulating heater cables, tracing tapes, and other types, are cables configured to provide heat in applications requiring such heat. Heater cables offer the benefit of being field-configurable. For example, heater cables may be applied or installed as needed without the requirement that application-specific heating assemblies be custom-designed and manufactured, though heater cables may be designed for application-specific uses in some instances.
In some approaches, a heater cable operates by use of two or more bus wires having a high conductance coefficient (i.e., low resistance). The bus wires are coupled to differing voltage supply levels to create a voltage potential between the bus wires. A positive temperature coefficient (PTC) material can be situated between the bus wires and current is allowed to flow through the PTC material, thereby generating heat by resistive conversion of electrical energy into thermal energy. As the temperature of the PTC material increases, so does its resistance, thereby reducing the current therethrough and, therefore, the heat generated via resistive heating. The heater cable is thus self-regulating in terms of the amount of thermal energy (i.e., heat) output by the cable.
Heater cables can exhibit high temperature variations throughout the cable, both lengthwise along the length of the cable and across a cross-section of the cable. These high temperature variations may be caused by small high-active heating volumes (e.g., PTC material) within the heater cable that can create localized heating, as opposed to heat spread over a larger surface area or volume. At the same time, other PTC material intended to be a heating volume may actually be thermally inactive, as no or limited current is dissipated therein. Additionally, in certain configurations, heater cables can be relatively inflexible, or substantially rigid, thus making installation of the heater cable difficult. Further, heater cables are typically not configured to provide varying selective heat output levels by a user.
Though suitable for some applications, such heater cables may not meet the needs of all applications and/or settings. For example, a heater cable that reduces temperature gradients may be desirable in some instances. Further, a heater cable that is capable of producing selectable but balanced heat output levels may be desirable in the same or other instances. Further still, for manufacturing efficiencies, a heater cable that achieves the above goal while utilizing structures and manufacturing methods of existing cables may be desirable.